Decompression control for internal combustion engine



D 3 1968 A. E. ANDERSON ETAL 3,418,992

DECOMPRESSION CONTROL FOR INTERNAL COMBUSTION ENGINE Filed July 19, 1967Patented Dec. 31, 1968 DECOMPRESSION CONTROL FOR INTERNAL COMBUSTIONENGINE Albert E. Anderson, Greenwich, Albert K. Newman, N-

roton Chris Schou, Greenwich, and James A. Ransom, Byram, Conn., andWalter Gorski, Armonk, N.Y., assignors to Textron Inc., Providence,R.I., a corporation of Rhotle Island Filed July 19, 1967, Ser. No.654,446 Claims. (Cl. 123182) ABSTRACT OF THE DISCLOSURE To facilitatestarting, an internal combustion engine is provided with a decompressionport located at a selected distance from the top of thecylinder so as todecrease compression during cranking of the engine. The port iscontrolled by a valve which is normally closed and which preferablycomprises a ball shaped valve member pressed against an annular valveseat. A unitary locking element holds the engine throttle control memberin selected position for starting and also holds the decompression valveopen. As soon as the engine starts, actuation of the throttle controlmember releases the locking element and thereby results in the automaticclosing of the decompression valve.

The present invention relates to internal combustion engines andparticularly to means for facilitating the starting of such engines. Theinvention is particularly applicable to small 2-cycle engines of thekind used for chain saws and other portable tools, lawn mowers, outboardmotors, etc.

In order to increase the horsepower rating and efiiciency of smallinternal combustion engines while keeping the weight of the engines at aminimum, it is desirable to operate the engines at a high compressionratio. The resistance offered by this high compression makes itdifficult to turn the engines over during cranking.

In order to facilitate the starting of internal combustion engines, ithas heretofore been proposed to provide means for relieving, at least inpart, the compression in the engine cylinder during cranking.Compression is relieved by means of a port in the engine cylinderpermitting the exhaust of gases from the cylinder during at least a partof the compression stroke. The decompression port must, of course, beclosed during normal operation of the engine as it would otherwiseresult in an objectionable loss of power and eificiency. Accordingly,the port is provided with valve means which is opened during cranking ofthe engine and must be closed after the engine has started.

While a decompression valve makes it easier to crank an internalcombustion engine, it is disadvantageous in that it requires theoperator to actuate an additional control device. This is particularlyobjectionable in handheld power tools such as chain saws. The operatoris required to hold the tool with one hand-preferably resting it on asupporting surfacewhile pulling the starter cable with the other hand.The addition of an extra control requiring the operators attentioncomplicates the starting procedure.

It is an object of the present invention to provide a unitary controlsystem by which a decompression valve is automatically held in an openposition during cranking of the engine and is automatically closed whenthe engine has started. The operator performs only those functions whichhe customarily performs in starting the engine. No additional action isrequired of the operator to effect a reduction in compression duringcranking of the engine and re-establishing full compression after theengine has started.

When the engine is running, it is important to maintain thedecompression valve tightly closed in order to avoid leakage of gaseseither during the compression stroke or the firing stroke of the engine.It has been found that with decompression valves of former design, it isdifficult consistently to avoid leakage. It is accordingly a furtherfeature of the invention to provide an improved decompression valvewhich is of simple construction, yet is highly effective in maintaininga fluid tight seal despite the high pressures to which the valve issubjected during operation of the engine.

The invention is applicable to engines provided with hand starting,e.g., by means of the usual pull cord. With hand starting, thedecompression system in accordance with the invention materially reducesthe effort required for cranking the engine. The invention is alsoadvantageous when applied to engines provided with self starters in thatthe reduced effort required for cranking the engine makes it possible touse smaller, lighter and less expensive starters.

The invention will be more fully understood from the followingdescription of preferred embodiments illustrated by way of example inthe accompanying drawings in which:

FIG. 1 is a fragmentary perspective view illustrating application of theinvention to an internal combustion engine,

FIG. 2 is a side view with portions broken away to show internalconstruction,

FIG. 3 is a view taken partly in section approximately on the line 33 inFIG. 2 with portions broken away to show the construction of thedecompression valve,

FIG. 4 is an enlargement of a portion of FIG. 3 and FIGS. 5 and 6 areviews corresponding to a portion of FIG. 3 but showing different valveconstructions.

In the drawings, there is shown a portion of an internal combustionengine 1 which, by way of example, may be a single cylinder, 2-cycleengine. The engine 1 is illustrated as having a cylinder 2 in which apiston 3 is reciprocable. A spark plug 4 provided in the cylinder headis connected by an insulated wire 5 to a magneto or other source ofelectricity.

The engine 1 is shown providing with a hollow grip or handle portion 7with which is associated a member 8 for controlling the speed of theengine, e.g., by regulating the supply of fuel to the engine cylinder.The engine control member 8 is shown in the form of a trigger which isapproximately L-shaped as seen from the side (FIG. 2) and is swingableabout a pivot pin 9 which projects laterally inside the hollow handle 7.The trigger 8 is connected to the carburetor or other fuel supply means(not shown) of the engine in such manner that the fuel supply, and henceengine speed, is increased when the trigger 8 is swung about its pivot 9in a clockwise direction as viewed in FIG. 2. A spring 10 acts on thetrigger 8 to swing it in a counter-clockwise direction to a position inwhich only suflicient fuel is supplied to the engine for it to run atidling speed.

In order to reduce the force required for cranking the engine to startit, the engine cylinder 2 is provided with a decompression port 12 whichis located in the cylinder wall at a selected distance from the head ofthe cylinder. The location of the decompression port is selected so asto permit the escape of a portion of the fuel-air charge in the cylinderduring the compression stroke while providing compression of theremaining portion of the charge after the top of the piston passes thedecompression port. By way of example, the decompression port is spacedfrom the head of the cylinder a distance equal to approximately topercent of the stroke of the piston. This location has been found toreduce to an acceptable value the force required for cranking the enginewhile still retaining sufficient charge and compression for reliablefiring of the engine.

The decompression port 12 is controlled by a valve 14 so that the portis open to provide decompression during starting but is tightly closedat other times to prevent leakage of gas from the cylinder when theengine is running. The decompression control valve 14 is shown ascomprising a valve housing 15 which is screwed or otherwise secured in aboss 16 provided on the cylinder wall. At its inner end, the valvehousing 15 is provided with an opening which is aligned with thedecompression port 12 in the cylinder wall and is surrounded by anannular valve seat 17. The valve seat is preferably of conical shapewith an angle of inclination of, e.g., about 45 (FIG. 4). The valvehousing 15 is hollow with a cylindrical bore 18 which is aligned withthe decompression port 12 but of larger diameter. A discharge port 19opens through the side wall of the housing at a location just outwardlyof the valve seat 17. The bore of the valve housing receives a plunger21 which is longitudinally slidable in the bore. A valve member 22,shown in the form of a spherical ball, is received in the bore betweenthe valve seat 17 and the inner end of the plunger 21. The ball 22 is ofhard corrosion resistant material, e.g., stainless steel, and is of adiameter which is less than that of the bore 18 but greater than theminimum diameter of the valve seat so as to engage the seat asillustrated in FIG. 4. A spring 23 supported on a fixed stud 24 engagesin a groove in the outer end of the plunger 21 and acts to press theplunger inwardly against the ball 22 and thereby press the ball intotight engagement with the valve seat 17 to close the decompression port12.

In accordance with the invention, unitary control means is provided forholding the fuel member 8 in proper position for starting andsimultaneously holding the decompression valve 14 in open position. Asillustrated by way of example in the drawings, the control meanscomprises locking means for releasably locking the fuel control member 8in selected position and connections between the locking means and thedecompression valve 14 to hold the valve open against the action of thespring 23 when the locking means is in locked position. The lockingmeans is shown in the form of a push-button 25 having a head portion 26and a stem portion 27 which is slidable in a bushing 28 extendingthrough a hole in one side wall of the hollow hand grip portion 7. Atits inner end,

the stem 27 is provided with a reduced portion terminating in a head 29of approximately the same cross sectional dimensions as the stem. A coilspring 31 surrounding the stem 27 acts between the side wall of the handgrip portion 7 and the head 26 to bias the push button to an outerposition as shown in solid lines in FIG. 3.

The locking element 25 is so located and proportioned that when the fuelcontrol member 8 is moved to a position to provide the desired amount offuel for starting the engine and when the push button 25 is pushedinwardly against the action of spring 31 to the position shown in dottedlines in FIG. 3, the head portion 29 at the inner end of the stem 27engages a web portion 32 on the fuel control member 8 so as to hold thepush button in its inner position and thereby hold the fuel control memher 8 in engine starting position.

The locking element 25 is suitably connected to the plunger 21 of thedecompression valve 14 so as to hold the plunger out against the forceof spring 23 and thereby hold the valve in open position when thelocking element is in locked position as indicated by broken lines inFIG. 3. In the example illustrated in the drawings, the connection is bymeans of a lever 35 having an intermediate portion which is rotatablysupported by a bracket 36 secured to a stationary portion of the engine,e.g., by screws 37. An arm a at one en f the lever 35 extends into ahole 38 provided in the plunger 21 near its outer end. An arm b at theother end of the lever 35 extends into an opening 29a in the headportion 26 of the locking element 25. The shape and location of thelever 35 are such that when the locking element 25 is pushed inwardly toits locked position as shown in broken lines in FIG. 3, the lever isrotated in the bearing provided by bracket 36 so as to swing the arm 35ain a counter-clockwise direction as seen in FIG. 3 and thereby move theplunger 21 outwardly against the bias of its spring 23. The valve member22 is thereby released from its seat 17 to open the valve. The effectivelength of the lever arm 35b is greater than that of arm 35a to provide amechanical advantage valve Without requiring excessive pressure on thepush button 25.

In preparation for starting the engine, the operator grasps the handle 7and, with his middle finger, applies pressure to the trigger 8 to swingit about its pivot 9 in a clockwise direction as viewed in FIG. 2. Withhis forefinger, he then pushes the locking element 25 to its innerposition and then releases the trigger 8 which, under pressure of thespring 10, returns toward idle position until the web portion 32 engagesthe reduced portion of the stem 27 of the locking element 25. Engagementof the head portion 29 on the inner end of stem 27 with the web portion32 of the trigger 8 retains the locking element 25 in locked positionand thereby holds the trigger S in position to supply the proper amountof fuel for starting. Movement of the locking element 25 to lockedposition has simultaneously opened the decompression valve 14 by reasonof the connections provided by the lever 35. The engine is then readyfor starting and is suitably cranked either by hand or by a starter. Assoon as the engine starts, the operator applies pressure to the trigger8 to regulate the speed of the engine as desired. The Web portion 32 ofthe trigger 8 is thereby disengaged from the head 29 at the inner end ofstem 27 of the locking element so that the locking element is moved byits spring 31 to its outer position as shown in solid lines in FIG. 3.By reason of the interconnection provided by lever 35, this movement ofthe locking element 25 releases the plunger 21 of the decompressionvalve 14 so that the plunger is moved inwardly by its spring 23 to pressthe ball 22 against the valve seat 17 and thereby close thedecompression port 12.

When the decompression valve is held open by the lever 35 duringstarting of the engine, a portion of the fuel-air charge is releasedthrough the decompression port 12 and discharge port 19 during a portionof each compression stroke. The exhaust port 19 of the decompressionvalve 14 may, if desired, be connected to the crank case of the engineso as to return the discharge fuelair charge to the crank case.Alternatively, the discharge port 19 may be connected to the exhaustsystem of the engine. However, in practice it has been found that theamount of fuel-air mixture discharged through the decompression portduring starting of the engine is so small that it can be dischargeddirectly to the atmosphere without any objectionable effects.

The ball 22 which constitutes the valve member of the decompressionvalve 14 is self-centering and is also free to rotate--when not beingpressed by the plunger 21. Presumably by reason of such rotatability ofthe ball, the valve has been found to he self-cleaning so as to assuregas tight closure of the decompression port at all times when the valve14 is closed. Objectionable leakage of gas from the cylinder is therebyavoided.

While it has been found in practice that gas pressure inside thecylinder is suflicient to unseat the ball 22 when the plunger 21 iswithdrawn by the lever 35, means can be provided if desired forpositively withdrawing the ball from its seat when the plunger 21 ismoved outwardly. Such an arrangement is illustrated by way of example inFIG. 5 in which the plunger 21 is shown provided at its inner end withportions 40 which extend past the mid;

point of the ball and are restricted so as to cage the ball whileleaving it free to rotate and free to move laterally sufficiently to beself-centering.

Another form of the decompression valve is illustrated in FIG. 6. Avalve plunger 41 corresponding to the plunger 21 illustrated in FIGS. 1to 5 is divided into two portions namely, an outer portion 41a and aninner portion 41b which constitutes a valve member. The outer portion41a is provided with an opening 42 to receive the arm 35a of the lever35 and with a transverse groove to receive a spring 23. The innerportion 41b of the plunger is rotatable relative to the outer portion41a. Hence, although the outer portion is held against rotation by thelever arm 35a and spring 23, the inner portion 41b is free to rotate.The two portions of plunger 41 are shown rotatably connected with oneanother by a reduced portion 43 on the inner end of the outer plungerportion 41a fitting sufficiently freely in a corresponding recessprovided in the outer end of the inner plunger portion 41b to permitfree rotation. The inner plunger portion 41b has a reduced portion 44 ofsmaller diameter than the inner diameter of the bore 18 of the valvehousing. At its inner end, the inner plunger portion 41b has afrustoconical portion 45 adapted to seat on the valve seat 17 and a tipportion 46 adapted to project into the decompression port 12 to keep itclear of carbon or other deposits. It has been found that by reason ofthe rotatability of the inner plunger portion 41b constituting a valvemember, the valve is self-adjusting and self-cleaning so as to maintaina fluid tight seal when the valve is in closed position.

While preferred embodiments of the invention have been illustrated byway of example in the drawings and have been herein particularlydescribed, it will be understood that the invention is not therebylimited to the particular examples shown.

What we claim is:

1. Control means for an internal combustion engine having a cylinder anda hand grip, said control means comprising a decompression port in saidcylinder, a normally closed compression relief valve closing said port,an engine fuel control member associated with said hand grip andoperable to control the supply of fuel to said engine, locking means forreleasably locking said fuel control member in selected position forstarting said engine, said locking means being movable between a lockingposition and a released position and means connecting said locking meanswith said valve to hold said valve in open position when said lockingmeans is in looking position.

2. Control means according to claim 1, in which said compression reliefvalve comprises a valve seat, a ballshaped valve member adapted to seaton said seat and spring pressed means normally pressing said valvemember on its seat.

3. Control means according to claim 2, in which said spring pressedmeans comprises a longitudinally slidable plunger and spring meanspressing said plunger toward said valve member.

4. Control means according to claim 3, in which said valve membercomprises a ball rotatably secured to an end of said plunger.

5. Control means according to claim 1, in which said locking meanscomprises a movable plunger and spring means urging said plunger towardreleased position, said plunger and fuel control member havingcooperating latch means for holding said plunger in looking position,said latch means being releasable by movement of said fuel controlmember in a direction to increase engine speed.

6. Control means according to claim 1, in which said compression releasevalve comprises a valve seat, a rotatable valve member adapted to seaton said seat and spring pressed means normally pressing said valvemember onto its seat.

7. Control means according to claim 1, in which said compression releasevalve comprises a valve seat, a valve housing having a bore aligned withsaid seat and a plunger longitudinally movable in said bore, saidplunger comprising an outer non-rotating portion an dan inner rotatableportion having a valve surface adapted to seat on said seat.

8. Unitary control means for an internal combustion engine having acylinder with aside wall and a head and a piston reciprocable in saidcylinder, said control means comprising a manually operable startingcontrol member which controls a starting function of the engine and ismovable between a starting position for starting the engine and arunning position when the engine has been started and is running, adecompression port located in the side wall of the cylinder and spacedfrom the head of the cylinder a distance equal to about 15% to 25% ofthe stroke of the piston, a normally closed compression relief valve forclosing said port, and means connecting said starting control memberwith said valve to hold said valve in open position when said startingcontrol member is in starting position.

9. Control means according to claim 8, in which said compression reliefvalve comprises an annular valve seat surrounding said port, a rotatableself-centering valve member seating on said seat to close said port andmovable outwardly from said seat to open said port and spring meansbiasing said valve member to closed position.

10. Control means according to claim 9, in which said valve member has aportion adapted to project into said decompression port to keep it clearof engine deposits.

References Cited UNITED STATES PATENTS 521,443 6/1894 Shepperd 1231822,440,483 4/ 1948 Mennesson 123182 2,625,924 1/ 1953 Friedlob 1231822,742,380 4/1956 Peters 123182 2,778,349 1/1957 Thommen 123-l822,922,436 1/1960 Brash 123-182 XR 2,947,300 8/1960 Trapp 123-182 WENDELLE. BURNS, Primary Examiner.

